Wraith (Puella Magi Madoka Magica)

Summary

After Madoka's sacrifice, curses and grief were forced to take a new form in the multiverse, known as Wraiths. At first, it was thought by magical girls and Incubators that Wraiths were beasts consuming on human lives as well as an indirect consequence of the Law of Cycles (If Homura Akemi's accounts were real).

Wraiths, in truth, were made to prevent massive amounts of emotional energy from potentially damaging the universe, as well as to be a "food source" for magical girls.